Integration of devices with higher density and higher degree of integration has been generally increasingly demanded in the production of electronic devices requiring submicron micromachining, represented by very-large scale integrated circuits (VLSIs). More and more strict requirements have therefore been made on photolithographic technologies as processes for fine patterning. Independently, electronic components, such as liquid crystal display devices, integrated circuit devices, and solid-state image sensors, use various films such as protective films (overfilms) for preventing deterioration and damage of the components; interlayer dielectric films for insulating layered interconnections from each other; planarizing films for planarizing the surfaces of devices; and dielectric films for maintaining electrical insulation. Of such electronic components, thin-film transistor (TFT) liquid crystal display devices as representative of liquid crystal display devices are produced in the following manner. Initially, a back substrate is prepared by forming a polarizer on a glass substrate; forming a transparent electroconductive circuit layer made typically of indium-tin oxide (ITO) and thin-film transistors (TFTs) on the glass substrate; and covering these components with an interlayer dielectric film. Independently, a front substrate is prepared by forming a polarizer on a glass substrate; patterning a black matrix layer and a color filter layer on the glass substrate according to necessity; and sequentially forming a transparent electroconductive circuit layer and an interlayer dielectric film. The back substrate and the front substrate are arranged so as to face each other with the interposition of spacers, and a liquid crystal is encapsulated in between the two substrates to give a TFT liquid crystal display device. Photosensitive resin compositions (photoresist compositions) for use therein should excel in transparency, thermal stability, and developability and should give coatings with smooth surfaces.
As techniques for achieving higher sensitivity of resists, there are well known chemically amplified resists using light-activatable acid generators acting as photosensitizers. By way of example, a resin composition containing a light-activatable acid generator and a resin containing epoxy-containing structural units is exposed to light, to allow the light-activatable acid generator to generate a protonic acid, and the protonic acid acts to cleave the epoxy group to induce a crosslinking reaction. This makes the resin insoluble in a developer to form a pattern. Additionally, a heat treatment is conducted after light exposure to allow the acid to move in the resist solid pattern, and the acid thereby acts to catalytically amplify chemical changes typically of the resist resin. Thus, the resist can have a dramatically higher sensitivity as compared to known resists having a photo-reaction efficiency (reaction per one photon) of less than 1. Most of currently developed resists are chemically amplified resists, and the chemical amplification mechanism should essentially be employed for the development of high-sensitivity materials that correspond to light irradiation sources having shorter and shorter wavelengths.
Dielectric films to be arranged in thin-film transistor (TFT) liquid crystal display devices and integrated circuit devices are generally made from radiation-sensitive resin compositions, because they should undergo fine patterning or microprocessing. Such radiation-sensitive resin compositions should have high radiation sensitivity, so as to produce dielectric films with high productivity. The dielectric films for use in production of liquid crystal display devices and integrated circuit devices should also have superior solvent resistance. This is because dielectric films, if being not so resistant to solvents, may suffer from swelling (blistering), deformation, and delamination from the substrate by the action of organic solvents, and this may significantly impede the production of liquid crystal display devices and integrated circuit devices. Additionally, dielectric films arranged typically in liquid crystal display devices and solid-state image sensors should have high transparency according to necessity.
There has been proposed a vinyl copolymer resin having epoxy groups and carboxyl groups in side chains as a curable resin which is used in the above-mentioned applications and excels in storage stability and curing properties (for example, Patent Document 1). The curable resin has epoxy groups in side chains and permits crosslinking (epoxy crosslinking) by the action of a crosslinking agent having a functional group reactive with epoxy group. Independently, there has been proposed a vinyl copolymer resin as a curable resin for use in the above-mentioned applications. This resin has carboxyl groups in side chains, and an epoxy compound having a polymerizable unsaturated group has been added to part of the carboxyl groups (for example Patent Document 2). The resulting curable resin has polymerizable unsaturated groups in side chains and thereby permits radical crosslinking using a radical initiator.
However, there have been known few vinyl copolymer resins that have both epoxy groups and carboxyl groups in side chains, in which an epoxy compound having a polymerizable unsaturated group is added to part of the carboxyl groups. This is because, if such an epoxy compound having a polymerizable unsaturated group is reacted with a vinyl polymer having both epoxy groups and carboxyl groups in side chains, the epoxy groups originally contained in the vinyl polymer intramolecularly react with the carboxyl groups also contained in the vinyl polymer, and the resulting resin suffers from gelation during reaction, or a solution of the resin becomes excessively viscous, to fail to give a desired curable resin.
Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 2006-193718
Patent Document 2: Japanese Unexamined Patent Application Publication (JP-A) No. 2000-191737